Massive galaxy clusters, such as MACS J1149.6+2223 shown here, can act as cosmic lenses, magnifying the light from distant background objects. Here, one of these clusters is showing off a distant exploding star. Photograph by NASA, ESA, and T. Treu (UCLA), P. Kelly (UC Berkeley) and the GLASS team; S. Rodney (JHU) and the FrontierSN team; J. Lotz (STScI) and the Frontier Fields Team; M. Postman (S